Lock nut and method of manufacture

Abstract: A low profile lock nut (10) for receiving a threaded bolt therein includes a body portion (12) having a threaded axial bore (14) extending through it with first and second opposite ends, a crown member (16) for providing a predetermined degree of flexibility, at least in a radial direction, to at least one of the first and second ends of the body portion, and an engagement member on at least one portion of the bore (14) positioned a pre-determined distance from each of the first and second ends respectively for engaging the threads of the bolt without distorting them and for co-operating with the crown member (16) to provide a desired installation torque as well as a desired removal torque. Typically such a lock nut (10) is formed by compressing it with a component transverse to its axis to provide the threaded bore (14) with a waisted or elliptical configuration.

Description: This invention relates generally to lock nuts for use with threaded bolts, and more particularly, to a lock nut formed in one-piece with a relatively low profile which provides a relatively low installation torque yet a high removal torque, even after repeated cycles of installation and removal of the lock nut from the bolt. Lock nuts which resiliently deform upon being threaded onto a bolt typically are of a relatively high profile and include some type of deformation of the nut. An example of such a lock nut is disclosed in U.S. Patent No. 4,990,043 which discloses a lock nut having a rigid body and a plurality of flexible locking beams projecting from one end of the rigid body. The locking beams are separated by slots so that upon engagement with a bolt the beams deflect outwardly and provide a resistance force to the bolt threads and reduce loosening of the lock nut from vibrations. That patent also discloses a sleeve integrally formed with one end of the rigid body of the nut where the threaded bore of the sleeve is deformed into a slightly oval configuration along the entire length of the bore. Such a lock nut, however, not only provides a substantially high profile which prevents its use in many applications, but also is substantially stiff since the bore is deformed along its entire length which inhibits installation and removal. DE-C-465059 discloses a fastening including a nut, bolt and a lock nut formed of a resilient material which is threaded onto the bolt to prevent movement of the nut. It therefore would be desirable to provide a one-piece low profile lock nut which provides a low installation torque yet a high removal torque, even after repeated removal of the lock nut. According to a first aspect of this invention a low profile lock nut for receiving a threaded bolt, comprises: a body portion having a threaded axial bore extending there-through, said body portion and said threaded bore having first and second opposite axial ends; crown means which is integral with extends from and encircles one end of the body portion which has a lesser wall thickness than the body portion to provide a pre-determined degree of flexibility, at least in a radial direction with respect to said axial bore, to the one end of said body portion, said threaded bore extending through said crown means; and, engagement means on a portion of said bore extending through said body portion and spaced a pre-determined distance from the other end of the body portion and the free end of the crown means, the engagement means having an inner dimension (A) less than that of the threaded bore at the other end of the body portion for lockingly engaging the threads of the bolt upon installation thereto without distorting the bolt threads, the lesser wall thickness of the crown means permitting flexure of the body portion at the engagement means to provide a low installation torque and a relatively high removal torque. The crown portion of the lock nut is substantially flexible to provide a spring action and enable threaded engagement with the bolt while providing the desired low installation and high removal torques. Preferably the crown portion has a pre-determined preferably scalloped configuration which provides a desired degree of flexibility to the crown portion. The bore of the lock nut is preferably re-configured to provide axial and radial movement of threads at a pre-determined position along its length at a distance from the ends of the bore to provide the bolt thread engagement portion. The engagement portion engages the bolt threads without distorting them and co-operates with the flexible crown portion to enable outward expansion of the nut and provide a spring force to the bolt threads which provides the desired low installation and high removal torques. After repeated cycles of installation and removal of the lock nut from the bolt, the installation and removal torques remain substantially constant. This particularly is important in applications where parts are routinely substituted or removed and re-installed for cleaning or inspection. According to a second aspect of this invention, a method of making a low profile lock nut comprises: providing a body portion having an axial bore therethrough; forming a crown portion having a pre-determined degree of flexibility, at least in a radial direction with respect to said axial bore, integrally with extending from and encircling one end of said body portion with said bore extending axially through said crown portion and with the wall thickness of said crown portion being less than that of said body portion; providing threads within said axial bore, said threads extending between a free end of the crown and the other end of the body portion; and, deforming at least a portion of said bore in said body portion and spaced a pre-determined distance from the other end of the body portion and the free end of the crown portion, the deformed portion having an inner dimension (A) less than that of the threaded bore at the other end of the body portion for lockingly engaging the threads of a bolt upon installation thereto without distorting the bolt threads, the lesser wall thickness of the crown portion permitting flexure of the body portion at the deformed portion to provide a low installation torque and a relatively high removal torque. A particular example of a lock nut and its method of manufacture will now be described with reference to the accompanying drawings, in which:- FIG. 1 is a perspective view illustrating one way of tapping and deforming lock nuts according to the teachings of the present invention; FIG. 2 is a longitudinal cross-sectional view of a lock nut of the invention taken along line 2-2 of FIG. 1 and in the direction indicated illustrating the different diameters of the threaded axial bore after deforming the lock nut; FIG. 2A is a longitudinal cross-sectional view of another embodiment of the lock nut of the invention illustrating a hexagonal shaped threaded axial bore; FIG. 3 is a top plan view of a lock nut of the invention before being deformed illustrating the substantially constant circular diameter of the axial bore; FIG. 4 is a top plan view of the nut of FIG. 2 as it is being deformed illustrating the elliptical shape obtained by the axial bore; FIG. 4A is a top plan view of the nut of the embodiment of FIG. 2A; and FIG. 5 is a bottom plan view of the nut of FIG. 3 before being deformed. Referring to FIGS. 1 and 2, the lock nut of the invention generally is designated by the reference numeral 10. The lock nut 10 preferably is formed from metal, has a very low profile and substantially includes a body 12 having a threaded axial bore 14 and a crown portion 16 formed on one end of the body portion 12. It is to be noted, however, that the particular material and shape of the lock nut 10 can vary so long as it functions as described herein. Preferably, to form the lock nut 10, the crown portion 16 is formed on one end of the body 12 in a cold forming operation or the like. As FIG. 1 illustrates, the threaded axial bore 14 then is provided by a tap 18. The lock nuts 10 then are conveyed for deformation, such as by compressing or crimping, which preferably is provided by rollers 20 in an in-line process which may leave slight indentations (not illustrated) on the exterior of the body 12. Compression of the lock nut 10 distorts a portion of the axial bore 14 into a slightly elliptical or oval shape as illustrated in FIGS. 2 and 4. The preferred mode of compressing or crimping is accomplished by rollers 20 contacting the body 12 substantially perpendicularly to the axis of the nut. However, alternatively the crown portion can be contacted directly at two or more opposed sections of the crown resulting in the shape shown in FIGS. 2A and 4A. Details of the axial bore 14, crown portion 16 and the co-operation of these elements will be provided herein. It is to be understood, however, that the method of manufacturing the lock nut 10 can vary. Briefly, in use, the shape of the crown portion 16 provides a pre-determined degree of flexibility to one end of the body 12 which typically does not face a threaded bolt (not illustrated) during installation or use. Upon engagement of the end of the axial bore 14 opposite the crown portion 16 with the threaded bolt, the bolt threads initially engage the first few threads of the bore 14 which substantially are circular in shape. Upon continued advancement of the lock nut 10 on the bolt, the bolt threads engage the compressed elliptical portion of the axial bore 14. Due to the flexibility of the crown portion 16, the axial bore 14 expands to its original circular shape upon continued advancement of the lock nut 10. Thus, the crown portion 16 functions similar to a spring member and applies an initial low installation torque yet a high retention torque or resisting force to the bolt threads without causing deformation of the bolt threads. As FIG. 2 illustrates, the body portion 12 includes a first bolt entrance end 22 and a second opposite bolt exit end 24. The axial bore 14 is threaded and extends between the first and second ends 22 and 24. As FIG. 3 illustrates, to enable gripping of the lock nut 10 with a tool, such as a wrench, the external periphery of the body portion 12 preferably is formed to include a plurality of wrench flats 26. Preferably, six wrench flats 26 are provided having six corresponding hex points 28, one hex point 28 between each wrench flat 26. Initially, before forming the crown portion 16 on the body 12, the wrench flats 26 and hex points 28 preferably extend along the entire length of the body portion 12 from the first end 22 to the second end 24. As FIGS. 2 and 3 illustrate, the crown portion 16 is illustrated positioned on the second end 24 of the body 12, but can be positioned on the first end 22, or both, if desired. The crown portion 16 is provided as a continuous member about the periphery of the lock nut 10 and includes a plurality of concave or conical indentations 30 formed thereon which provide the crown portion 16 with a "scalloped" shape about its external periphery and the desired degree of flexibility to the crown portion 16. Preferably, six concave indentations 30 are provided, one each to correspond in radial position with a respective wrench flat 26. The concave indentations 30 taper toward the second end 24 to form the conical shape and include a substantially thin wall portion 32 positioned proximate a mid-point of each concave indentation at the second end 24 of the body 12. To vary the flexibility of the crown portion 16, the material, configuration and dimensions of the lock nut 10 can vary so long at it functions as described. As FIG. 2 illustrates, after compression or crimping of the lock nut 10 by the rollers 20, the axial bore 14 obtains its greatest elliptical shape proximate the impact point with the rollers 20 having a minor axis indicated by "A". Due to the flexibility of the crown portion 16, the bore 14 also is slightly elliptical as it passes through the crown portion 16 having a minor axis indicated by "B". As the bore 14 passes through the first end 22 of the body 12, however, it substantially maintains its original circular configuration due to the thickness of the first end 22 of the body 12 and has a diameter indicated by "D". The circular diameter "D" enables easy starting of the lock nut 10 on the bolt. Preferably, the minor axis "A" is positioned proximate the mid-point of the bore 14 which roughly corresponds to the interface between a bottom of the crown portion 16 and the remainder of the body 12, but can vary so long as it is positioned away from the ends of the bore 14. The minor axis "A" is smaller than the minor axis "B" proximate the end of the bore 14 at the second end 24 of the body 12. Additionally, the diameter "D" of the bore 14 proximate the first end 22 of the body 12 is greater than the minor axis "B". Thus, the bore 14 initially is circular with a diameter "D" proximate the first end 22 of the body 12, becomes elliptical toward its centre with a minor axis "A" and expands back outwardly to an elliptical shape with a minor axis "B" which is greater than the minor axis "A". It is to be noted that the resistance force provided by the crown portion 16 which provides the low installation and high removal torque remains substantially constant, even after repeated cycles of installation and removal of the lock nut 10 from the bolt. The following tables illustrate torques obtained in testing with the lock nut 10. One In/lbs corresponds to 60 mm/kg. GROUP I Sample No. FIRST-ON (In/Lbs) FIRST-OFF (In/Lbs) FIFTH-OFF (In/Lbs) 1 38 35 30 2 50 42 38 3 43 38 30 4 40 38 32 5 50 48 35 HIGH 50 48 38 LOW 38 35 30 AVG. 44.2 40.2 33 GROUP II SAMPLE No. FIRST-ON (In/Lbs) FIRST-OFF (In/Lbs) FIFTH-OFF (In/Lbs) 1 60 50 40 2 38 30 28 3 30 28 20 4 50 40 30 5 30 20 20 HIGH 60 50 40 LOW 30 28 20 AVG. 41.6 35.2 27.6 The above test results were obtained using an In/Lb hand torque wrench. In each case, the initial "First-On" torque was taken after three full bolt threads were exposed. The "First-Off" torque was obtained with one complete turn counter clockwise. The "Fifth-Off" torque was obtained after five cycles of turning on and removing with the reading taken with the fifth removal.

Claims: A low profile lock nut (10) for receiving a threaded bolt, comprising: a body portion (12) having a threaded axial bore (14) extending there-through, said body portion (12) and said threaded bore (14) having first and second opposite axial ends; crown means (16) which is integral with extends from and encircles one end of the body portion (12) which has a lesser wall thickness than the body portion to provide a pre-determined degree of flexibility, at least in a radial direction with respect to said axial bore (14), to the one end of said body portion (12), said threaded bore (14) extending through said crown means (16) ; and engagement means on a portion of said bore (14) extending through said body portion and spaced a pre-determined distance from the other end of the body portion (12) and the free end of the crown means (16), the engagement means having an inner dimension (A) less than that of the threaded bore (14) at the other end of the body portion for lockingly engaging the threads of the bolt upon installation thereto without distorting the bolt threads, the lesser wall thickness of the crown means (16) permitting flexure of the body portion at the engagement means to provide a low installation torque and a relatively high removal torque. A lock nut as defined in claim 1, wherein said crown means (16) include a continuous periphery and a predetermined configuration to provide said degree of flexibility. A lock nut as defined in claim 1 or 2, wherein an exterior periphery of said body portion (12) includes a plurality of wrench flats (26) radially positioned thereabout and said crown means (16) include a plurality of concave surfaces (30) corresponding in number to said wrench flats (26), each concave surface (30) being radially positioned to substantially correspond with a respective wrench flat (26) and being tapered toward the end of said body portion on which it is formed so that a thin region is formed on each concave surface proximate its mid-point and the respective end of said body portion to provide the desired degree of flexibility. A lock nut as defined in any preceding claim, wherein said engagement means includes providing a portion of said bore (14) with a substantially elliptical configuration. A lock nut as defined in any preceding claim, wherein said crown means and said engagement means provide for maintaining at least one of said installation and removal torques substantially constant after repeated installation and removal of the lock nut from the bolt. A method of making a low profile lock nut comprising the steps of: providing a body portion (12) having an axial bore (14) therethrough; forming a crown portion (16) having a pre-determined degree of flexibility, at least in a radial direction with respect to said axial bore (14), integrally with extending from and encircling one end of said body portion (12) with said bore (14) extending axially through said crown portion (16) and with the wall thickness of said crown portion (16) being less than that of said body portion (12); providing threads within said axial bore (14), said threads extending between a free end of the crown (16) and the other end of the body portion; and, deforming at least a portion of said bore (14) in said body portion (12) and spaced a pre-determined distance from the other end of the body portion (12) and the free end of the crown portion (16), the deformed portion having an inner dimension (A) less than that of the threaded bore (14) at the other end of the body portion for lockingly engaging the threads of a bolt upon installation thereto without distorting the bolt threads, the lesser wall thickness of the crown portion (16) permitting flexure of the body portion (12) at the deformed portion to provide a low installation torque and a relatively high removal torque. A method as defined in claim 6, including providing said crown portion (16) with a continuous periphery and a pre-determined configuration to provide said degree of flexibility.

Inventors: SCHULENBURG STEVEN H, THURSTON RAYMOND L, SCHULENBURG, STEVEN H., THURSTON, RAYMOND L.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1994
Main classification: F16B39
IPC codes: F16B39, F16B29, B21K1